Circuit Switching

This blog is about computer networks, the Internet, and packet switching not about telephone networks and circuit switching. However, it is important to understand why the Internet and other computer networks use packet switching rather than the more traditional circuit-switching technology used in the telephone networks. That's why, we now give a brief overview of circuit switching.

"Multiplexing in Circuit-Switched Networks" figure demonstrates a circuit-switched network. In this network, the four circuit switches are interconnected by four links. Each of these links has n circuits, so that each link can support n simultaneous connections. The hosts (for instance, PCs and workstations) are each directly connected to one of the switches. When two hosts want to communicate, the network establishes a dedicated end-to-end connection between the two hosts. (Conference calls between more than two devices are, of course, also possible. But to keep things simple. let's suppose for now that there are only two hosts for each connection.) Thus, in order for Host A to send messages to Host B, the network must first reserve one circuit on each of two links. Because each link has n circuits. for each link used by the end-to-end connection, the connection gets a fraction 1/n of the link's bandwidth for the duration of the connection.

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